This invention relates to a method of forming an artificial reef unit under water, to an artificial reef unit so formed, and to elements for use in its construction.
It is well known to form support structures such as roadways, canals or river or bank linings and the like from a material having a honeycomb structure, i.e having a plurality of compartments or cells divided by dividing walls, each compartment or cell being filled with a suitable filler material. Examples of such materials for use in these support structures are Hyson-Cells from M and S Techical Consultants and Services (Pty) Limited, Geoweb from Presto Products Co, Tenweb from Tenax Corp, Armater from Crow Company, Terracell from Webtech Inc, Envirogrid from Akzo Nobel Geosynthetics Co and Geocells from Kaytech.
However, there is always a need for new methods of utilising this tube material.
According to a first aspect of the invention there is provided a method of forming an artificial reef unit under water on a base which comprises the steps of:
(1) locating a tube of a flexible material divided by dividing walls of a flexible material into an array of compartments or cells running the length of the tube, the compartments being arranged in rows and columns so that the tube divided by the dividing walls has a honeycomb structure, with a first end of the tube on the base and a second end of the tube above the first end of the tube and under water;
(2) securing the tube in position on the base using one or more flexible and/or rigid elements attached to a fixed object, e.g the base; and
(3) at least partially filling some or all of the compartments with a filler material so that at least some of the compartments are adjacent two or more other compartments filled with a filler material to support and be supported by the adjacent compartments.
A single artificial reef unit may be formed as described above to provide an artificial reef. However, in general, a plurality of artificial reef units will be formed in series, abutting or overlapping one another, or with spaces there between, to form the artificial reef.
The artificial reef unit of the invention may be used in a fresh water environment or, preferably, in the sea.
When the artificial reef unit is intended for under the sea or in an environment where there are waves, the side of the tube facing open water, i.e facing away from the shore, is preferably suitably profiled, e.g curved to dissipate wave energy by deflecting the waves. For example, a portion of the tube from the first end of the tube to a mid point of the tube is preferably convex in cross-sectional shape and a portion of the tube from the mid point of the tube to the second end of the tube is preferably concave in cross-sectional shape so that a wave striking this side of the tube is rolled up and over away from the shore. Alternatively the side of the tube facing open water may be sloped so that a wave striking this side of the tube is slowed and/or broken up.
In addition, the side of the tube facing the shore may also be sloped or curved if desired.
In step (2) of the method of the invention, any suitable means may be used to secure the tube in position on the base. For example, a flexible string or a rigid stay may be located through a row of compartments at or near each outer row of the array and a flexible string or a rigid stay may be located through a column of compartments at or near each outer column of the array. The ends of the strings may then be attached to fixed objects, such as for example the base, to support the tube in position.
Alternatively, a semi rigid or rigid stay may be attached to each corner of the tube, with the free ends of each stay being anchored to the base. In this case the stays may later be removed for re-use, once step (3) is complete.
The use of flexible strings or rigid stays to support a tube in position is described in more detail in co-pending application PCT/IB 99/00965, which is incorporated herein by reference.
In one embodiment of the invention, when the artificial reef unit is designed to dissipate wave action or to protect a shore, in step (3), it is preferable that all the compartments are substantially filled with the filler material.
In a second embodiment of the invention, when the artificial reef unit is designed to provide an area for the propagation of marine life, it is preferable that some or all of the compartments are only partially filled with the filler material so as to leave spaces for fish and other marine creatures.
In this second embodiment, the edges of the compartments at the second end of the tube may be frayed to make the artificial reef unit more marine friendly. The frayed edges resemble fronds of seaweed.
The filler material may be sand or any other material from the area where the artificial reef unit is located. Alternatively, suitable filler material can be imported from an external source.
The nature of the filler material in the various compartments of an artificial reef unit may be varied. For example some compartments, particularly those abutting a fixed structure such as a pier or wall or pipeline, may be filled with a cementitious material, while others of the compartments may be filled with sand or gravel.
The tube and the dividing walls may be made from any suitable flexible material. Although the material must possess some degree of flexibility, the degree of flexibility may range from very flexible up to semi-rigid. The flexible material may be for example a plastics material such as for example a co-extruded or a bi-axially extruded plastics material; a plastics mesh material; a plastics laminate material such as for example a laminate of a plastics material and a metallic material or a textile material; a metallic material; a woven or non-woven textile material; a paper or cardboard material; and the like.
The flexible material is preferably a suitable plastics material.
The tube may have any suitable height and any suitable compartment size. For example, the height of the tube may range from 100 mm to 10 m and each compartment may have a wall length of from 5 mm up to 2 m. In certain instances, it may be desirable for the outer walls to be longer than the inner dividing walls at the first end. This allows for the extra material to be tucked underneath one or more of the compartments to prevent loss of filler material by undermining.
The compartments in the tube may have any suitable cross-section, such as triangular, square, hexagonal or octagonal, but preferably have a square cross-section, i.e each compartment is defined by four walls of substantially equal length.
The cross-sectional size of the compartments may reduce or increase in size in the tube. For example, the compartments may be of three different sizes, with the cross-sectional size of the compartments in a first row and in one or more rows adjacent the first row being greater than the cross-sectional size of the compartments of one or more rows intermediate the first and last rows of compartments, which in turn have a greater cross-sectional size than the cross-sectional size of the compartments in the last row and in one or more rows adjacent the last row of compartments.
The use of compartments with different cross-sectional sizes is described in more detail in co-pending application PCT/IB99/00967 which is incorporated herein by reference.
According to a second aspect of the invention there is provided an artificial reef unit formed as described above.
According to a third aspect of the invention there is provided an artificial reef formed from a plurality of artificial reef units, placed in series, each artificial reef unit being formed as described above.
According to a fourth aspect of the invention there is provided a method of forming an artificial reef unit under water on a base which comprises the steps of:
(a) locating a tube of a flexible material divided by dividing walls of a flexible material into an array of compartments or cells running the length of the tube, the compartments being arranged in rows and columns so that the tube divided by dividing walls has a honeycomb structure, with the axes of the compartments substantially parallel to the base;
(b) constricting the compartments at a point between the two ends of the tube;
(c) securing the tube in position on the base using flexible and/or rigid elements attached to a fixed object, e.g the base; and
(d) at least partially filling some or all of the compartments with a filler material to hold the tube in position on the base to form the artificial reef unit.
According to a fifth aspect of the invention there is provided an artificial reef unit formed as described above.